As an optical receiver applied to a conventional PON system, for example, there is a burst digital optical receiver disclosed in a Patent Document 1 described below. The optical receiver includes a photoelectric conversion element, an automatic-threshold-control (ATC) circuit, and a discriminator. The photoelectric conversion element converts a received burst digital light signal into an electric signal; a preamplifier that outputs a first positive phase signal and a first negative phase signal with a differential output obtained by amplifying this electric signal to a predetermined level. The ATC circuit outputs a second positive phase signal and a second negative phase signal in a reverse-phase relation with the second positive phase signal, the second positive phase signal being obtained by averaging a value of the first positive phase signal and a value obtained by peak-holding the first negative phase signal and the second negative phase signal being obtained by averaging a value of the first negative phase signal and a value obtained by peak-holding the first positive phase signal at signal time or a value of an offset voltage set higher than this value at no-signal time. The discriminator decides, from the second positive phase signal and the second negative phase signal, a logical value “0” at the no-signal time of the burst digital light signal, and performs logical decision according to an intermediate value of amplitude values of the burst digital light signal and outputs logical values “1” and “0” at the signal time.
In the above optical receiver, the preamplifier connected to the photoelectric conversion element controls a gain of the preamplifier itself according to a detection level obtained by subjecting an optical output signal level from the photoelectric conversion element to peak detection at high speed. The auto threshold control circuit connected to an output side of the preamplifier inputs a discrimination output (level) to the discriminator at the post-stage. The discrimination output is obtained by averaging a signal output of a differential output signal outputted from the preamplifier and a selection circuit output generated based on two detection outputs obtained by performing peak detection (PD) and bottom detection (BD).
Patent Document 1: Japanese Patent Application Laid-Open No. H9-181687.